The present invention refers to a ventilation system for household appliances, in particular washing machines.
As known, some household appliances, in particular various types of washing machines, are equipped with a ventilation system based on the-use of a blower or fan; typically, these systems are assembled on those dishwashing machines with a final drying step for the crockery and pots at the end of the washing, favoured by air forced ventilation inside the washing tub.
The action of the above fan is intended for improving removal of the steam produced inside the washing tub and obtain an improved drying than obtained by more conventional solutions (such as leaving the crockery inside the machine for a few minutes, during which the steam is partially removed through a “condensing effect” exerted by the tub walls, and causing the steam to be partially expelled through appropriate venting outlets).
Common dishwashing machines fitted with forced drying systems have the fan usually located inside the door or in the gap formed between one of the tub side walls and the corresponding wall of the machine outer cabinet; as a result, the fans used to this purpose should have very small dimensions or anyway a flattened form, though providing good air outlet sections.
Some known solutions have the fan fitted with a shutter operating on the fan suction duct from the tub, which is apt to isolate the former from the latter to avoid water inlet during the wash steps; at wash end, this shutter is actuated to open the above suction duct, the fan is started and both the dampness and steam can be sucked outside the tub and either condensed or expelled in the environment outside.
The movable shutter employed in the above systems usually is in the form of a half disk or disk with appropriate slits, which is swivelling or angularly movable for opening the fan suction duct.
Examples of this shuttering means are described in EP-A-0 521 815 and GB-A-2.274.772.
This shutter configuration as a disk or half disk has some drawbacks.
A first drawback is the hydraulic sealing between the shutter and the suction duct being poorly reliable, due to the lack of gaskets between these parts. Theoretically, special gaskets may be provided on the shutter or suction duct for sealing improvement, but in this case the system would necessarily require a significant actuation force to produce the angular or rotating movement of the shutter; this is due to the need of overcoming the frictions caused by the shutter sliding on the sealing gaskets of the suction duct or by the frictions caused by the sealing gaskets of the shutter sliding on the surfaces of the suction duct.
Besides originating the above frictions, such sliding may also lead to a high wear of the gaskets with time.
Shutters according to common art have a poor efficiency from a standpoint of fluid mechanics; this drawback is due to the form of common shutters, which are substantially in the form of a disk, i.e. with a flattened shape causing a certain resistance to air circulation.
Additionally, shuttering means according to common art do not provide for a complete opening of the fan suction duct, due to their configuration like a half disk or disk with slits; it is actually clear, that in case of half-disk shutters the air outlet section will be at the most equal that of the half disk, whereas in the instance of disk shutters with slits, the air outlet section will be at the most equal than of the slits.